Altitude, Sweat & Hydration

By Jason Tullous

Training at altitude has many advantages, and there are key aspects to your training that you must pay close attention to as you acclimate in order to make the most of those advantages.  One of these aspects is hydration.

High altitude environments typically center around very arid climates. As human beings, every inhalation we make must be fully hydrated.  Drier high altitude environments will require your body to supply most of that hydration.  Couple this with your body’s natural reaction to altitude (more breaths per minute) and you can quickly dehydrate without realizing it.

Why is all this important?  Hydration is the number one reason for fatigue during exercise.  Even at a 2% loss in hydration, you can expect a significant performance decrease.

Typically, we assume 20-30 ounces per hour is enough for most athletes, but when we are acclimating to altitude, there is a need to increase hydration. How much do we increase that number?

There are general guidelines suggesting 0.185 ounces per pound of body weight per hour, but this is just a “general” recommendation and, as everyone knows, there can be tremendous variation based on individual physiology. To properly predict how much fluid you need to replenish your hydration, you need to keep in mind factors like heat, humidity, metabolic rate, intensity of training, body core temperature, body surface area, etc. That’s a lot of science and a lot of calculations. Testing in a laboratory setting can be cost prohibitive and, even if you have good numbers out of that setting to work from, everything changes as the altitude changes and your fitness changes (typically the fitter you are, the higher your sweat rates).

But there is a simplified, cost-effective approach using basic technology that most of us have ample access to: a scale. Weight lost in your workouts is water weight.  So weigh yourself (dry) before and after your workout.  Note the environmental conditions to get familiar with how your body reacts to conditions. Then – and most important – know how much you drank during the workout and how many minutes the workout lasted. When these three variables are known, you then have the ability to create the equation for your sweat rate.

We have a nice outline and equation below. Remember one pound of water equals 15.4 ounces or 1 kilogram equals 1 liter of water. Now it’s time to experiment. Find out what your needs are and how good you are at managing your hydration by doing the pre-exercise and post exercise weigh-ins, then note your consumption during your workout.  I suggest measuring for a week in similar environmental conditions to get a good guideline for yourself.  By the end of the week, you’ll know before you even get on the scale how well you did during your workout.

Sweat Rate Calculator

A. Weight Pre exercise                                          ________lbs
B. Weight Post exercise                                        ________lbs
C. Change in Body weight (= A-B)                       ________lbs
D. Volume of fluid consumed                             ________oz
E. Sweat Loss (=(C*15.4)+D))                               ________oz
F. Exercise time                                                       ________min
G. Sweat Rate (=E/F )                                              ________oz/min

All measurements in ounces (oz) and pounds (lbs)  To convert to metric system:

1 kilogram = 2.2 pounds
29.6 mL   = 1 ounce

Remember this is very important as hydration is the number one reason for fatigue during exercise.  Stay ahead of the curve and DRINK! Do note that your sweat rates will change with changing environments (ex. winter versus summer).  Also note that if you are just changing to a higher temperature environment, your sweat rates should increase in 10-14 days as you acclimate to the warmer temperatures.

Happy drinking and don’t forget the electrolytes!

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